T cells play an important role in controlling tumor growth and mediating tumor rejection in vivo. Identification of several classes of MHC class I-restricted tumor antigens from melanoma as well as other cancers has led to the initiation of clinical trials using these identified T cell epitopes. While these studies hold the promise of effective treatment of patients with metastatic cancer, the exclusive use of CD8+ T cells may not generate an optimal anti-tumor immunity. Increasing evidence from both human and animal studies indicates that CD4+ T (helper) cells play a central role in initiating and maintaining the host immune responses against cancer, but the lack of such knowledge of MHC class II-restricted tumor antigens is a major hurdle for developing more effective cancer vaccines. The long-range goal of this study is to dissect immune components of tumor immunity, to understand the mechanism by which CD4+ T cells regulate immune responses, and to develop effective cancer vaccines for the prevention and therapeutic treatment of patients with cancer. The central hypothesis is that MHC class II-restricted tumor antigens induce tumor-reactive CD4+ T cells, which provide critical help for priming and activation of CD8 T cells, the major effector cells for tumor destruction. Thus, the combination of CD4+ with CD8+ T cell epitopes will further augment anti-tumor immune responses. The rationale for the proposed research is that, once it is known how tumor immunity is regulated by MHC class II restricted CD4+ T cells, CD4+ T cell helper peptides/antigens will be effectively incorporated in cancer vaccine regimen for the preventive and treatment of patients with cancer. The proposed research is built on a novel genetic system we originally developed. We have generated unique resouces (tumor-specific CD4+ T cell lines or clones), and established experimental animal models. To test our central hypothesis, we will further improve the genetic cloning system and identify MHC class II-restricted tumor antigens as immune targets. We will evaluate the immunogenicity and role of DR2-restricted T helper peptides in protective immunity in DR2-Tg mice. We will also develop novel vaccine strategies to enhance CD4+ T cell responses in an attempt to eradicate tumor. It is anticipated that these studies will advance the field of immunotherapy of cancer and provide a foundation of the development of novel approaches for effective cancer vaccines.